A vehicle is provided with at least one tank for storing a liquid which is required for operating the vehicle. At the same time, a sensor arrangement for determining a filling level of the liquid in the tank is associated with the tank. However, it should be taken into account that a system that comprises the tank as well as the sensor arrangement is subject to manufacturing tolerances as well as to changes occurring over the lifespan of the system. For that reason, it is usually the case that when the tank is almost full or almost empty, it is not always possible to ascertain an absolutely correct value of the filling level by means of the sensor arrangement and also to indicate this via a display device to the driver of the vehicle.
It is therefore necessary to provide tolerances in a region in which the tank is almost full, as well as in a region in which the tank is almost empty, when the tanking indicator is installed. If for example fuel is stored in the tank in advance for driving the motor vehicle, it is then possible for instance to prevent a situation when the vehicle stalls due to a lack of fuel.
The tolerances should in this case be set in such a way that the fuel level indicator reliably indicates that the tank is empty if the supply of fuel has been exhausted. The fuel level indicator must also indicate with reliability the status when the tank is full.
However, unfavorable characteristics of the fuel level indicator may occur as a result of preset and/or applied tolerances. So for example, it is possible that the fuel level indicator indicates that the tank is empty although there still are for example 3.5 to 5 liters of fuel in the tank. This amount of fuel is not visible to the driver, which creates an additional burden for the vehicle resulting in a lower traveling range.
In addition, the fuel gauge can also indicate that the tank is full even though this is not the case. In general, the fuel gauge does not indicate the real filling level in a linear manner.
From document DE 10 2007 030 992 A1 is known a method for detecting a fuel filling level in a tank of a motor vehicle with an internal combustion engine. In this case, a fuel filling level sensor signal is determined by a fuel filling level sensor. In addition, a calculated fuel filling level is determined as a function of a fuel amount that is consumed by the internal combustion engine. A corrected fuel level signal is thus provided depending on the fuel filling level signal and the calculated fuel filling level.
A method for monitoring a digital fuel filling level sensor for a tank that is subjected to movements is described in the document DE 10 2008 009 154 A1. In this case, occurrences of sloshing at a filling height around a sensor position in the tank are used to arrive at a conclusion about a functional capability of tank filling sensor.
In the document 10 2010 043 936 A1 is described a method for determining the filling level of a movable tank. This method comprises discrete pins provided with filling level sensors arranged at different filling levels, so that sensor signals obtained from pins arranged at different heights are interpolated and filtered to provide a quasi-continuous signal. In this case, sloshing zones are defined around the pins, within which sloshing of the liquid stored therein occurs during the movement of the tank, so that the filling level can be inferred from the signal obtained during the occurrences of the sloshing events.